Home > Articles

  • Print
  • + Share This
This chapter is from the book

Formula for Capacitance

The formula for capacitance is fairly straightforward (see Equation 3-10). It is purely a function of the geometry of the plates and the material between the plates. Some capacitors (e.g., ceramic ones) are made up of several layers of plates, and the n – 1 term accounts for this.

Equation 3-10

03equ10.gif


where:

εr

= relative dielectric coefficient (air = 1, FR4 ≅ 4)

A

= area of each plate (in2)

d

= distance between plates (in)

n

= number of plates

Applying this formula to a PCB made from FR4 with εr = 4, 3-inches square, and with power and ground planes spaced 10 mils apart would lead to a capacitance of

049equ01.gif


  • + Share This
  • 🔖 Save To Your Account